How Muscles Work

Knowing how muscles work will help you better understand the benefits of exercise, the importance or rest, and the smartest way to train to achieve your fitness goal.

Our bodies have three major types of muscles: cardiac, smooth, and skeletal. When most people think of muscles, we think of skeletal muscles. Skeletal muscles are what we depend on to walk, lift, run, and perform the majority of our daily movements. These muscles convert chemical energy to mechanical energy, so in order to understand how muscles work, we’re going to need to talk about some chemistry...

The cells of our body use something called Adenosine Triphosphate (ATP) as an immediate source of energy (less than 30 seconds). Some short running races like the 100-yard dash use 100% ATP as an energy source.

Beyond 30 seconds of all-out exercise, the muscles need to use their stores of glycogen. From the glycogen, the muscles continue to get their source of ATP. In the process of forming ATP from glucose, lactic acid is formed as a byproduct. Too much lactate in the muscles and the blood leads to muscle fatigue. If the body is getting enough oxygen (aerobic exercise), then the body’s aerobic energy system will kick in (i.e. fat burning). If the exercise remains ‘all-out’ or anaerobic exercise, then muscle fatigue will ensue in about 3 – 5 minutes.

For aerobic exercise, the body converts both glycogen and fatty acids to energy. These fuel sources are found in the muscle’s inherent energy stores and in the blood as it circulates through the body. As blood circulates through the body, fatty acids are used for fuel and waste products are carried away from the muscles. The level of intensity determines the ‘mix’ of glycogen and fatty acids. For slower paced aerobic exercise, more fat is utilized for energy over the muscle’s stores of glycogen.

How can this help me (you might ask)?

Both anaerobic and aerobic exercise have benefits to our muscular health. Muscles need stress and rest to grow stronger – anaerobic exercise is a good stressor and can help the muscles increase their glycogen storage capacity. Aerobic exercise makes your muscles more efficient at burning fat. Longer duration aerobic exercise provides a significant calorie burn and reduction of body fat, as well.

Building muscles through exercise can have far-reaching impacts in your daily life – beyond the immediate growth of the muscle itself. More muscle leads to a higher metabolism or basal metabolic rate...so you’ll be burning more fat even while you sleep! Stronger muscles can also prevent injuries, aches and pains. For example: Stronger abdominal muscles will take strain off your lower back muscles and will help reduce lower back pain; and stronger quadriceps muscles will help take the strain off a weakened Iliotibial (IT) band.

Knowing how muscles work, what exercises target the muscles you predominantly use, and what stretches can de done to keep these muscles loose and flexible is an important step to building a successful exercise routine into your fitness plan.